The present invention generally relates to tilt sensors, and more particularly to a an electrolytic tilt sensor that is manufactured using standard printed circuit board fabrication techniques.
Traditional tilt sensors generally use some mechanism that is influenced by the local gravitational field in order to determine the level of tilt from some horizontal reference position. One type of sensor uses a weighted, rotating pendulum that is attached to a potentiometer or variable capacitor. Accuracy of this type of sensor is limited by the design and cost of the shaft and bearing about which the pendulum swings. For many applications, a pendulum type tilt sensor is too large, heavy, and expensive. A second type of tilt sensor measures the gravitational force on a conventional or micro-machined weighted beam. Although these types of tilt sensors can be small and relatively inexpensive, the electrical output varies as the sine/cosine of the tilt angle whereupon the relation between tilt angle and electrical output varies considerably throughout the range of the sensor. A third type of tilt sensor uses variations of the traditional xe2x80x9cbubble level.xe2x80x9d If the fluid in this type of sensor is electrically conductive, electrodes placed in contact with the fluid result in an electrical response related to the tilt angle. The changing electrical impedance between the contacts can be converted to a useable output with proper signal conditioning electronics.
Historically, most of these types of sensors have been hand assembled using precious metal electrode wires, glass housings, and lead wires that have been sealed and attached by hand.
Thus, these types of sensors require skilled labor assembly, which tends to be costly. More recently, glass housed tilt sensors have been made by machine, which lowers their fabrication costs, but are only available in limited configurations. Even with lowered manufacturing costs, tilt sensors that have glass housings are very fragile and still expensive to mount in an instrument housing. Some manufacturers sell sensors mounted in machined metal housings. However, sensors mounted in metal housings are relatively expensive, and too large for many applications.
A need therefore exists for a tilt sensor that is inexpensive to manufacture, small, and easily mounted. A further need exists for a tilt sensor that can be massed produced with very repeatable performance characteristics.
A method for manufacturing an electrolytic tilt sensor comprises: a) forming sensing electrodes on a generally planar surface of a dielectric substrate; b) forming a reference electrode on the surface; c) mounting a housing to the substrate so that the sensing electrodes and the reference electrode are contiguous to a volume defined between the housing and the substrate; d) forming a fluid tight seal between the housing and the substrate; e) injecting an electrolytic fluid into the volume; f) sealing the electrolytic fluid in the volume; and g) forming an electrical circuit on the substrate for generating an output signal representing the angle of the dielectric substrate with respect to a gravitational field, wherein the electrical circuit includes an oscillator mounted on the surface.
In another aspect of the invention, an electrolytic tilt sensor, comprises: a) a dielectric substrate having a first planar surface; b) a first sensing electrode affixed to the dielectric substrate and having a second planar surface entirely in contact with the first planar surface; c) a second sensing electrode affixed to the dielectric substrate and having a third planar surface entirely in contact with the first planar surface; d) a reference electrode affixed to the dielectric substrate and having a fourth planar surface entirely in contact with the first planar surface; e) a housing mounted to the dielectric substrate so that the first and second sensing electrodes and the reference electrode are contiguous to a volume defined between the housing and the dielectric substrate; f) a fluid tight seal formed between the housing and the dielectric substrate; g) an electrolytic fluid contained within the volume; and h) electrical circuitry mounted on the dielectric substrate and electrically coupled to the first and second sensing electrodes, and to the reference electrode for generating an electrical signal representing an angular displacement of the electrolytic fluid with respect to the dielectric substrate, wherein the electrical circuitry includes an oscillator mounted on the first planar surface.